Climate Change and the Causes of War

New study makes Pentagon report all the more alarming.


Periods of warfare in ancient China peaked during climate crises (in grey).

A fascinating article in the latest edition of Discover magazine discusses a study in the journal Human Ecology. Earth scientist David Zhang and colleagues at the University of Hong Kong used high-resolution palaeo-temperature reconstructions and compared that to the complete historical record of warfare in eastern China.

As Zhang et al. state in their study (subscription required):

There is no academic consensus on the causes of historic cycles of war and peace. Historians cite government mismanagement and concomitant social turmoil; military scientists and politicians emphasize power imbalances among competing groups or entities; psychologists and biologists relate warfare to innate human aggressiveness; while the Marxists hold that warfare is the unavoidable consequence of class struggle. However, none of these explanations adequately accounts for war–peace cycles from a macro-historical perspective.

Instead what the researchers find is that warfare is better explained as “an adaptive ecological choice under circumstances of population growth and resource limitation.”

Over the past millennium, eastern China suffered from periodic ecological stress and a significantly reduced anthropocentric carrying capacity during climatic cooling. Since the expanded population encouraged by the previous warm phase could not be sustained, famine and nationwide uprisings, predominantly mobilized by peasants, were seemingly fueled during cold phases. Such domestic chaos weakened state power, which in turn invited northern nomadic invasions.

This study further supports the thesis that Jared Diamond promoted in Collapse, that the leading factor in the demise of past societies has been an inability to cope under ecological crises. When such calamity strikes and governments can't provide for their needs, the population revolts or governments push into neighboring territories to access essential resources.

This should raise a large warning flag for our own society as several recent crises are largely due to natural calamities (think Katrina) or resource shortages (think Iraq). Human caused global climate change is expected to cause great fluctuations in seasonal temperatures and areas that have formerly been the “bread baskets” of the world could one day (perhaps relatively soon) be unable to support agriculture.

In the 2003 Pentagon report on global warming entitled An Abrupt Climate Change Scenario and Its Implications for United States National Security the authors had an eerily similar conclusion for our own society to that which Zhang and colleagues found about ancient China.

“As famine, disease, and weather-related disasters strike due to the abrupt climate change, many countries’ needs will exceed their carrying capacity. This will create a sense of desperation, which is likely to lead to offensive aggression in order to reclaim balance.”

“The United States and Australia are likely to build defensive fortresses around their countries . . . to hold back unwanted starving immigrants.”

I don't think this requires any further commentary from me.